DOT texas-impactos sobre puentes ensayos.pdf

Protección de puentes ante impactos vehiculares

1. Nicholas Nemec, P.E.
Bridge Division
DESIGNING BRIDGES
FOR VEHICULAR
COLLISIONS

2. Designing Bridges for Vehicular Collisions
TYPES OF VEHICULAR COLLISIONS:

–Over Height Impacts



–Lateral Impacts



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3. Designing Bridges for Vehicular Collisions
Over Height Impacts:

–Occurs when upper portion of “load” comes in contact with lower portion
of one (or more) superstructure beams/girders

–Most frequent type of collision


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4. Designing Bridges for Vehicular Collisions
Over Height Impacts:

Causes-
–Loads taller than legal limit (in route without a permit)
–Permits granted without proper investigation of route clearances
–Misinterpretation of the permit route
–Inaccuracies in “true” clearance vs “recorded”
–Errors in preparing/securing the load for travel
–Errors in Design Assumptions
–Overlooked Design Flaws


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5. Designing Bridges for Vehicular Collisions
Over Height Impacts:

Errors in Design Assumptions-
–Avoid designing to the absolute minimum clearance (16’-6”)

•Superstructure depths can not be predicted that precisely (especially during
bridge layout phase)
•Prohibits adding overlay to the lower roadway in the future
•Prohibits bridge from being widened in the future (due to cross slope being
extended)
•Future loads (10,15 20+ years) will not be shorter than those of today

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6. Designing Bridges for Vehicular Collisions
Over Height Impacts:

Errors in Design Assumptions-
–Ignoring the minimum (16’-6”) requirement for “special circumstances”

•Discoveries (such as oil/natural gas) in a new area suddenly subject the
highway to a “new breed” of traffic, which it was not designed to handle
•Assuming that lower roadways in urban areas are not subject to over height
loads



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7. Designing Bridges for Vehicular Collisions
“This is a city it street…it will never see an over height load!!”



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Take a closer look
here…

8. Designing Bridges for Vehicular Collisions
“This is a city it street…it will never see an over height load!!”



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9. Designing Bridges for Vehicular Collisions
Over Height Impacts:

Over looked Design Flaws-
–Forgetting to step back and see “the big picture”



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10. Designing Bridges for Vehicular Collisions
Typical PLAN of an Intersection…


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11. Designing Bridges for Vehicular Collisions
Typical ELEVATION of the Intersection…


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12. Designing Bridges for Vehicular Collisions
Taking a step back…


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Take a look
here…

13. Designing Bridges for Vehicular Collisions
Taking a step back…


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This end of cap hangs over
the majority of the turn lane

14. Designing Bridges for Vehicular Collisions
Looking at the Bent Cap…

Approximate clearance looks like 14’(“H”) -1’(below ground)+~1’(on arc of
bent) = 14’ +/-
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15. Designing Bridges for Vehicular Collisions
Over Height Impacts:

One last thing……..



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16. Designing Bridges for Vehicular Collisions
Over Height Impacts: “BRIDGE PROTECTIVE BEAM WRAP”
Standard (BPBW)
•Issued as a Bridge Standard on July 10, 2013
•Is NOT A REPAIR DETAIL
•Intended for New Construction (can be used as a retrofit on some types of existing
superstructure types also)
•Intended for use on Bridges
with high probabilities of being
impacted by over height loads
•Used at the discretion of the
Engineer (no height
requirement for applicability)

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17. Designing Bridges for Vehicular Collisions
Over Height Impacts: “BRIDGE PROTECTIVE BEAM WRAP”
Standard (BPBW)
•Purpose is to prevent debris from falling on the roadway/traffic in the event that the
beam is impacted
•Is not intended to add strength to the beam to withstand an impact load
•After an impact, beam needs to be inspected and appropriate repairs made
just as without the BPBW



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18. Designing Bridges for Vehicular Collisions
Over Height Impacts: “BRIDGE PROTECTIVE BEAM WRAP”
Standard (BPBW)
•Located on the Bridge Standards page along with the issuing memo
•Contact Amy Smith (512-416-2261) for questions regarding BPBW



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19. Designing Bridges for Vehicular Collisions
Lateral Impacts:

–Occurs when a vehicle (tractor-trailer) veers off the designated roadway
and impacts the bridge structure (typically the column)

–Can result in very large lateral loads
to bridge column




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20. Designing Bridges for Vehicular Collisions
Lateral Impacts:

–Magnitude of damage is variable:


Minor Damage Loss of Substructure Collapse
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21. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Causes-
–Distracted Driver
–Fatigued Driver
–Tight horizontal clearance
–Inadequate protective barrier
–Difficult to predict probability of occurrence


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22. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Tight Horizontal Clearances:
–Avoid locating columns immediately next to roadway (when possible)




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This collision would not have occurred if the column
was located farther away from the roadway

23. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Tight Horizontal Clearances:
–Avoid locating columns immediately next to roadway (when possible)




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This is an Interstate Highway with columns located very
near the edge of roadway

24. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Inadequate Protective Barrier:
–Many times columns must be located near the roadway and a barrier is
used to protect the columns from impact




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25. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Inadequate Protective Barrier:


Inadequate Barrier Inadequate Barrier
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26. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Inadequate Protective Barrier:


No Barrier
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27. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Difficult to Predict:
–The root causes of the misdirection (driver fatigue and distraction) can
force the collision to occur at a location well off of the intended path of the
vehicle.
–Frequency of collisions (limited data) is not high enough to develop an
accurate statistical model that includes site specific variables
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28. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Difficult to Predict:
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Travel Path

29. Designing Bridges for Vehicular Collisions
Lateral Impacts:

Difficult to Predict:
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East Bound 
 West Bound
Truck was traveling WEST,
crossed median, crossed
East Bound Lanes and hits
column
Impact

30. Designing Bridges for Vehicular Collisions
Lateral Impacts:

So what do we do about designing for lateral impacts???

–AASHTO LRFD BRIDGE DESIGN SPECIFICATIONS 2012 gives us guidance
in Section 3.6.5-Vehicular Collision Force
–Tailored after research findings from Texas Transportation Institute (TTI)
“Guidelines for Designing Bridge Piers and Abutments for Vehicle
Collisions.” ---Technical Reports 9-4973-1 and 9-4973-2
–Accomplished three (3) tasks
•Determined a design force to represent a vehicle collision
•Identified the primary failure mode of a column subject to a collision
•Established criteria to evaluate the susceptibility of a given bridge to impact

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31. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Design Force
–Computer Simulation using a Finite Element Model (FEM)
–Several test matrices with following variables:
•Pier Diameter (24”, 36”, 48”)
•Impact Speed (40mph, 50mph, 60mph)
•Cargo Type (Deformable , Rigid)

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Greatest impact on force

32. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Design Force
–Computer Simulation using a Finite Element Model (FEM)
–Results (2 Peaks in Force vs Time curves):
•Engine block impact ~480 — 600 kips
•Cargo impact ~480 — > 2000 kips (due to instability of results)



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33. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Design Force
–Computer Simulation using a Finite Element Model (FEM)
–Test Case(FEM) : 36” Pier, 50 mph, deformable ballast:
•Engine block impact ~ 580 kips
•Cargo impact ~ 900 kips

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34. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Design Force
–Full Scale Testing
•Design and build a “Rigid Column” to stop the truck and measure forces


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35. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Design Force
–Full Scale Testing
•Design and build a “Rigid Column” to stop the truck and measure forces


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36. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Design Force
–Full Scale Testing
•Design and build a “Rigid Column” to stop the truck and measure forces
•Select variables for full scale test (50mph, deformable)
•Run the full scale test



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37. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Design Force
–Full Scale Testing
•Results: 50-ms Average results are what we care about
•Dynamic load is represented by an equivalent ~400 kips static load



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38. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Design Force
–Full Scale Testing
•Results: 50-ms Average results are what we care about
•Dynamic load is represented by an equivalent ~400 kips static load

•However, refined analysis of the data (due to energy used to deflect the column
elements) produce a dynamic load of 700 kips, which is represent by the static
approximate load of around 600 kips

•Max force was found to be located ~5’ above the ground




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39. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Failure Mode
–Examining past collisions
–Results: Shear Failure with 2 Shear Planes




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40. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Evaluation Criteria

AASHTO 2012, Section 3.6.5, commentary provides equation
C3.6.5.1-1: AF
HBP=2(ADTT)(P
HBP)365

AF
HBP = annual frequency of a given bridge pier to be hit
ADTT = the number of trucks in one day in one direction
P
HBP = the annual probability for a bridge pier to be hit by a heavy
vehicle

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41. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Evaluation Criteria

AASHTO 2012, Section 3.6.5, commentary provides equation
C3.6.5.1-1: AF
HBP=2(ADTT)(P
HBP)365

P
HBP is a based on the type of roadway:
=3.457x10
-9
for undivided roadways
=1.090x10
-9
for divided roadways in tangent sections
=2.184x10
-9
for divided roadways in horizontally curved
sections

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42. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Evaluation Criteria
–From TxDOT Bridge Design Manual, if AF
HPB is less than 0.001, do not
design for vehicle collision.
–If greater than 0.001, then collision must be considered by either:
•Provide a method to redirect or absorb the load
•Design the column to structurally resist the load

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43. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Evaluation Criteria
–Redirecting the Load:
•Protect with a structurally independent, ground-mounted 54-in. tall single slope
concrete barrier (or other 54-in. tall, Test Level 5 approved barrier equivalent) if
within 10 ft. from component

•Protect with a 42-in. tall single slope concrete barrier (or 42-in tall, Test Level 5
approved barrier equivalent) if more than 10 ft. from component

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44. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Evaluation Criteria
–Structurally Resisting the Load:

•600-kip equivalent static load
•Extreme Event II Load Combination
•Use 1.25 load factor for all dead loads and 0.5 load factor for live load,
considering live load only on the permanent travel lanes, not the shoulder lanes


•Assume load is resisted by 2 shear planes (multi column bents)
•Assume load is resisted by 1 shear plane (single column bents)




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45. Designing Bridges for Vehicular Collisions
Lateral Impacts:
Evaluation Criteria
–Structurally Resisting the Load:

•Usually the single column bents have sufficient mass to nominally resist the
collision force.

•The column of a single column bent does not need to be analyzed for the
collision load as long as it meets all of the following criteria:

–Gross cross section greater than or equal to 40 SF
–Smallest dimension is greater than or equal to 5 feet
–Transverse reinforcing of No 4’s @ 12” or No 4 spiral with 9” pitch




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46. Designing Bridges for Vehicular Collisions
Questions?



Contact Information:

[email protected]
[phone]




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